CROPNUT: increasing iron in cereals

铁和锌缺乏是全球健康问题，目前通过补充剂和强化计划来解决。在发展中国家，铁补充剂是援助方案的组成部分，防治贫血症是世界卫生组织的一项主要优先事项。在更近的家庭中，血清铁水平低在11-(2012年全国饮食和营养调查)的女性中普遍存在，这与铁摄入量低有关。为了解决铁缺乏的问题，所有在英国碾磨的面粉都在化学上添加了铁盐或铁粉，最高可达16.5毫克/公斤(英国面粉法规1998)。现代面包小麦中铁的自然变化被限制在白粉中6-13毫克/公斤的范围内。施肥实验表明，植物不会吸收多余的铁。因此，使用基因方法提高铁和锌水平，即所谓的生物强化，是提高我们饮食中矿物质水平的最可持续的方法，我们的饮食主要是几种主要作物。面包小麦中铁水平的有限变化被归因于许多因素。几个世纪以来，选择作物品种是为了产量，但代价是微量营养素含量。此外，小麦等多倍体作物在遗传上是缓冲的：可能改变某一性状的基因变异被同一基因的其他副本所掩盖，这使得选择新性状变得困难。此外，铁的水平受到植物的严格控制，以防止这种以游离离子形式有毒的金属的过度积累。最后但并非最不重要的一点是，谷物并没有进化到将大量矿物质添加到淀粉胚乳中，这是我们更喜欢吃的谷物部分。在巴尔克和乌伊实验室非常成功的合作中，我们最近发现，与预期相反，来自小麦或大麦的白色面粉中的铁和锌含量可以分别增加3倍和2倍。元素分析表明，白粉中的铁含量为16-17 mg/kg，接近法定强化要求，全麦面粉中的铁含量更高。这是通过顺式基因组学方法实现的：小麦植株是转基因的，但序列来自小麦本身。我们在小麦铁转运蛋白的前面放置了一个胚乳特异的调控序列。我们的结果表明，原则上，植物可以将更多的铁和锌引导到胚乳中，而不是天然的。此外，似乎没有对增长产生任何重大负面影响。虽然液泡铁转运蛋白的及时过表达在提高谷物中的铁和锌水平方面效果非常好，但我们还不明白为什么这一策略如此成功。毕竟，上调的基因是一个简单的运输器，而不是一个调节器。如果我们将交通流量类比，增加M25上的车道数量本身并不能改善交通流量。通道、路口等都需要拓宽，以增加交通流量，防止拥堵。此外，我们还发现该转运蛋白是铁的专一性转运体，不能转运锌。那么，为什么锌含量会增加呢？为了利用我们的发现进行生物强化，我们将研究高铁小麦品系矿物质转移增加背后的分子和细胞生物学变化。我们还将调查铁和锌的来源是什么，例如，植物是否从土壤中吸收了更多的铁，或者铁是否从植物的其他部分得到了更有效的再动员。然后，我们将利用这些信息来制定非转基因策略，以增加小麦和其他谷物中的铁和锌。铁和锌的生物利用率将通过向培养的肠道细胞提供消化的白面粉和面包来测试。综上所述，这些研究将极大地增强我们对养分运输的了解，为我们提供新的和非转基因的策略来提高小麦的营养质量，并为我们提供一种评估它们对人类营养的影响的方法。

Deficiencies in iron and zinc are global health issues, which are currently addressed by supplements and fortification programmes. In the developing world, iron supplements are an integral part of aid programmes and combatting anaemia is a major priority of the World Health Organization. Closer to home, low serum iron levels are prevalent in ~5% of females aged 11 - 64 (National Diet and Nutrition Survey 2012) correlating with low iron intake. To combat iron deficiency, all flours milled in the UK are chemically fortified with iron salts or iron powder up to 16.5 mg/kg (UK Flour Regulations 1998). The natural variation of iron in modern bread wheat is limited within the range of 6 - 13 mg/kg in white flour. Fertilization experiments have shown that extra iron is not taken up by plants. Therefore, increasing iron and zinc levels using genetic methods, known as biofortification, is the most sustainable approach to increase mineral levels in our diet which is dominated by a few staple crops.The limited variation in iron levels in bread wheat has been attributed to a number of factors. Over centuries, crop varieties have been selected for yield, at the cost of micronutrient content. Moreover, polyploid crops such as wheat are genetically buffered: gene variants that could change a certain trait are masked by other copies of the same gene, which makes it hard to select novel traits. In addition, iron levels are tightly regulated by plants to prevent over-accumulation of this metal that is toxic in its free ionic form. And last but not least, cereals have not evolved to put large amounts of minerals into the starchy endosperm, the part of the grain that we prefer to eat.In a very successful collaboration between the Balk and Uauy labs, we have recently found that, against expectations, iron and zinc levels in white flour from wheat or barley can be increased 3- and 2-fold, respectively. Element analysis showed that the iron levels of white flour were 16 - 17 mg/kg, similar to the legal requirement for fortification, and higher still in wholemeal flour. This was achieved by a cis-genics approach: wheat plants were genetically modified but the sequences are from wheat itself. We placed an endosperm-specific regulatory sequence in front of a wheat iron transporter. Our results show that, in principle, plants can direct much more iron and zinc to the endosperm than they do naturally. Moreover, there does not seem to be any major negative effect on growth. While the timely overexpression of the vacuolar iron transporter works remarkably well in boosting iron and zinc levels in grain, we do not yet understand why this strategy is so successful. After all, the up-regulated gene is a simple transporter and not a regulator. If we draw an analogy to traffic flow, increasing the number of lanes on the M25 does not per se improve traffic flow. Access roads, junctions and so on all need to be widened to increase traffic and prevent congestion. Also, we found that the transporter is specific for iron and cannot transport zinc. So why are zinc levels increased?To exploit our findings for biofortification, we will investigate the molecular and cell biological changes that underlie increased mineral transfer in the high-iron wheat line. We will also investigate what the source of iron and zinc is, for example if the plants take up more iron from the soil or whether the iron is more efficiently remobilized from other parts of the plant. We will then use this information to develop non-GM strategies to increase iron and zinc in wheat and other cereals. The bioavailability of the iron and zinc will be tested by offering digested white flour and bread to cultured intestinal cells. Taken together, these studies will greatly enhance our knowledge on nutrient transport, provide us with novel and non-GM strategies to increase the nutritional quality of wheat and give us a way to assess their impact on human nutrition.